Loop antennas are used in devices (e.g., radio tags) that exchange signals by means of radio such as RFID. Loop antennas are broadly classified into a planar type that uses a flexible printed circuit (FPC) or the like and a coil type. Typical examples in which planar-type loop antennas are used include IC cards used as tickets for means of transportation.
The requirements for IC cards include necessity to make the cards thin, necessity to possess a certain degree of flexibility, and the like. Furthermore, the IC card shown in FIG. 6 (see Japanese Patent Application Kokai No. 2004-13587), for example, has been proposed in the past to meet such requirements.
The IC card 100 shown in FIG. 6 comprises a film substrate 110 formed from a resin material, a loop antenna element 120 that is patterned on the surface of the film substrate 110, and a mounting part 130 to which the respective terminals of the loop antenna element 120 are connected. Moreover, the mounting part 130 is provided with a tuning capacitor for tuning the signal frequency of the loop antenna element 120 and an IC chip having memory.
Meanwhile, coil-type loop antennas are also used for devices which do not pose strict thickness restrictions that are required for IC cards used in cellular phones or the like having the RFID function.
Because a loop antenna requires a relatively large mounting surface area among the parts used in a device of this type for the application of this type, there are cases in which a loop antenna constructed in planar form such as that shown in FIG. 6 is hard to use. Here, if a loop antenna constructed in planar form, a problem occurs in that directionality is altered.
Furthermore, planar-type loop antennas using an FPC are expensive compared to coil-type loop antennas. Therefore, it is hard to use a planar-type loop antenna in some cases for cellular phones or the like, which have severe cost requirements. Incidentally, IC cards used as tickets for means of transportation or the like are lent by railway companies or the like in exchange with deposited money, so that the cost does not seem to be as big of an issue as in cellular phones. From such circumstances, not only planar-type loop antennas, but coil-type loop antennas are also used for IC cards used as tickets for means of transportation.
The IC card shown in FIG. 7 (see Japanese Patent Application Kokai No. H11-251509), for example, has been known in the past as such an IC card comprising a coil-type loop antenna.
The IC card 200 shown in FIG. 7 is formed by mounting a loop antenna element 220 that transmits and receives radio waves and a semiconductor chip 230 that performs information processing on a wiring board 210 having a wiring pattern formed on the front surface thereof. Furthermore, the loop antenna element 220 is electrically connected to the wiring board 210 by soldering the connecting terminals 221 of the loop antenna element 220 and the connecting lands 211 of the wiring board 210 to each other.
However, in the loop antenna of the IC card 200 shown in FIG. 7, because the loop antenna element 220 is connected to the wiring board 210 by soldering, a problem occurs in that a variance of approximately ±1 mm per each soldered portion is generated in the loop length of the loop antenna element 220 installed on the wiring board 210. The variance in the loop length of the loop antenna element 220 is especially prominent in cases where the loop antenna element 220 is a multiple loop.
Moreover, when the variance occurs in the loop length of the loop antenna element 220 installed on the wiring board 210, the resonant frequency of the loop antenna varies. Then, when the resonant frequency of the loop antenna varies, the transmission/reception distance of the loop antenna varies.